Two specific hypotheses concerning the effects of psychological stress on the cardiovascular system are proposed and tested. The first suggests that animals genetically predisposed to hypertension evince greater stress-induced cardiovascular and sympatho-adrenal medullary changes than animals genetically resistant to hypertension. The second postulates that stress paradigms which prevent the development of effective coping responses result in more pronounced cardiovascular and sympathoadrenal medullary alterations that stress paradigms which allow coping. To test these hypotheses, Dahl hypertension-sensitive and Dahl hypertension-resistant rats will be exposed to different stressful conditioning procedures. These rats, which evince opposite, genetically determined sensitivities to a variety of putative hypertensinogenic stimuli, will be compared with respect to their acute and chronic changes in blood pressure, heart rate and circulating catecholamine levels in anticipation of, during exposure to and during recovery from the stress exposure.